what is a resin used for? and for what purpose you use resin

The term "resin" as relates to models is a two part polyurethane liquid that cures by catalytic action and it is an exothermic process (sometimes very exothermic). There are literally over 100 types of this resin on the market, all with different viscosities, cure rates and physical properties once cured. Done correctly resin can yield incredible detail, done incorrectly you might as well start with a bar of soap and a jack knife to carve it because you either have a lump that vaguely resembles what it's supposed to be or you have more airbubble than resin. Like styrene kits all resin kits have certain kinds of defects specific to the medium. Resin requires CA or epoxy to bond and should be primed with an acrylic lacquer like Alclad or Mr. Surfacer. Generally the resins used for kits are more brittle than styrene so some care has to be taken when using tools like Xactos.

Contrary to popular and far too often repeated myths, resin dust IS NOT toxic, extermely dangerous, very hazardous or anything of that nature. Once properly cured resin is inert. The danger of resin dust is a simple mechanical danger common to ALL dusts, it can lodge in your lungs. Common sawdust and flour are far more dangerous than resin because you rarely think about the dust hazard let alone the explosion hazard, resin dust has much higher flashpoint than either sawdust or flour so your wife is more likely to blow up the kitchen than you are to blow up the workshop when working with resin.......you are however more likely to blowup the workshop with sawdust......

resin is a molding material much like plastic, but it is often higher quality and makes your models look way better, detail wise (in most cases). Resin dust is very harmful, though. So when sanding, use a respirator. Resin can be an AfterMarket item or even a whole kit. Resin is pourded in a way that there are virtually no mold seams and far more detail. To achieve this, however, the mold must have a pour stub, found at the bottom of a piece of molded resin. This can be removed with a razor saw and sandpaper. resin is a great medium to master, and the results look fantastic.

You can also create your own resin parts, I have not done so yet, so someone else may inform you further on that.